From 5cae667cafada8056b37bb912dd290eb3017dc5c Mon Sep 17 00:00:00 2001
From: Stephen Celis <stephen@stephencelis.com>
Date: Tue, 7 Sep 2021 10:21:15 -0400
Subject: [PATCH] Prefix should match when maxLength < match.count (#50)

* Prefix should match when maxLength < match.count

* cleanup

* wip
---
 Package.resolved                     |  2 +-
 Sources/Parsing/Parsers/Prefix.swift | 19 ++++++-------------
 Tests/ParsingTests/PrefixTests.swift |  6 ++++++
 3 files changed, 13 insertions(+), 14 deletions(-)

diff --git a/Package.resolved b/Package.resolved
index 8c3f8f8d85..a3e911222c 100644
--- a/Package.resolved
+++ b/Package.resolved
@@ -11,7 +11,7 @@
         }
       },
       {
-        "package": "swift-benchmark",
+        "package": "Benchmark",
         "repositoryURL": "https://github.com/google/swift-benchmark",
         "state": {
           "branch": null,
diff --git a/Sources/Parsing/Parsers/Prefix.swift b/Sources/Parsing/Parsers/Prefix.swift
index d79127c86b..b7e4ec52bc 100644
--- a/Sources/Parsing/Parsers/Prefix.swift
+++ b/Sources/Parsing/Parsers/Prefix.swift
@@ -148,19 +148,12 @@ where
 
   @inlinable
   public func parse(_ input: inout Input) -> Input? {
-    if let predicate = self.predicate {
-      let prefix = input.prefix(while: predicate)
-      let count = prefix.count
-      guard count >= self.minLength, self.maxLength.map({ count <= $0 }) ?? true else { return nil }
-      input.removeFirst(count)
-      return prefix
-    } else {
-      let prefix = self.maxLength.map(input.prefix) ?? input
-      let count = prefix.count
-      guard count >= self.minLength else { return nil }
-      input.removeFirst(count)
-      return prefix
-    }
+    var prefix = maxLength.map(input.prefix) ?? input
+    prefix = predicate.map { prefix.prefix(while: $0) } ?? prefix
+    let count = prefix.count
+    guard count >= self.minLength else { return nil }
+    input.removeFirst(count)
+    return prefix
   }
 }
 
diff --git a/Tests/ParsingTests/PrefixTests.swift b/Tests/ParsingTests/PrefixTests.swift
index 42ab140bd6..9acfc9e5d6 100644
--- a/Tests/ParsingTests/PrefixTests.swift
+++ b/Tests/ParsingTests/PrefixTests.swift
@@ -61,4 +61,10 @@ final class PrefixTests: XCTestCase {
     XCTAssertEqual("42", Prefix(...10, while: { $0.isNumber }).parse(&input))
     XCTAssertEqual(" Hello, world!", input)
   }
+
+  func testPrefixLengthFromWhileSuccess() {
+    var input = "42 Hello, world!"[...]
+    XCTAssertEqual("4", Prefix(1, while: { $0.isNumber }).parse(&input))
+    XCTAssertEqual("2 Hello, world!", input)
+  }
 }